Display panels such as liquid crystal display panels are now used in a wide application range from business to household applications. So far, display panels of various sizes, specifically from a small size for mobile phones, game machines, or the like to a large size for televisions, outdoor information displays, or the like, have been fabricated, and practically used.
In recent years, display panels having an additional function, for example, capable of displaying three-dimensional (3D) images as well as conventional two-dimensional (2D) images, or providing images that change with the viewing angle, have been attracting attention. In some of these devices, a member for providing such an additional function is disposed in front of a conventional display panel.
In particular, some liquid crystal display panels for certain usages, which include thin glass substrates for a thinner design, are provided with a glass plate or a transparent plastic plate in front thereof for the purposes of, for example, display panel surface protection and crack resistance especially in the case of a large display panel. Another purpose of such a glass plate disposed in front of a display panel is to build a model that meets the need for a display design with a hard, glaring, and flat surface.
In a conventional model, such a plate (referred to as “flat plate”), specifically, a glass plate, a plastic plate, a 3D panel, or the like is disposed in front of a liquid crystal display panel with a certain space from the liquid crystal display panel surface to which a polarizer is provided. Such a space, however, is a cause of surface reflection at the refractive index interface between the liquid crystal display panel side (inner) surface of the flat plate and air or at the refractive index interface between the polarizer and air. This also causes problems such as double exposure images or reflection of an image that interferes with displayed images. These problems are attributed to the difference in refractive index between substances, and therefore can be solved by forming an antireflection coat on the surfaces at which reflection occurs, or replacing the air layer with a material having a refractive index close to that of the flat plate or the polarizer. These techniques can be seen in the case that a resin is filled in a space between a liquid crystal display panel and a flat plate (see Patent Literature 1) or in the case that a plasma panel and a flat plate is adhered by a resin disposed therebetween (see Patent Literature 2).
As other examples of improved display panels with a flat plate, there may be mentioned a display panel in which a flat plate is adhered using a resin having an elastic modulus after cure of not lower than a certain value to avoid stress that is generated when the resin is cured and shrinks, and may form streaks on the display (see Patent Literature 3), and in the case that a flat plate and a liquid crystal display panel are adhered together with a photocurable resin that is enclosed in a dam-like structure surrounded by a guide between the flat plate and the liquid crystal display panel (see Patent Literature 4).
When a flat plate is attached to a display panel by charging a photocurable resin composition in a space between the flat plate and the display panel, and photocuring the resin, there is the following disadvantage. For example, in the case where there is apart that blocks light, the light blocking part prevents a sufficient amount of light from reaching the entire resin, and therefore leaves apart of the resin uncured. One strategy to overcome this disadvantage is that the photocurable resin is cured by light irradiation from the outside to a lateral face to certainly allow even an area of the photocurable resin composition behind the light blocking part to be cured (see Patent Literatures 5 and 6). Another strategy to cure the area of the photocurable resin composition behind the light blocking part is to use a thermal polymerization initiator to allow the resin to be cured not only by photopolymerization but also by thermal polymerization (see Patent Literature 7). Use of both photopolymerization and thermal polymerization regardless the presence or absence of light blocking parts is also under development (see Patent Literature 8).